1. Field of the Invention
This invention relates to ceiling grid runners and associated assembly details for suspended ceiling grid systems. More specifically the runners utilize a composite structure comprising an appropriately compounded thermoplastic polymer reinforced by strategically placed steel members. The product is corrosion free and upgraded visuals can be produced.
2. Description of the Prior Art
The I-beam principle for efficiently utilizing materials has been known for many years. A recent example is a wooden I-beam fabricated from reconstituted wood in such a way to maximize strength to weight ratio at the same time being able to use secondary quality wood that is unfit for use in more traditional wood construction products.
The traditional all metal suspended grid products use the I-beam principle to the greatest extent possible within the constraints of the existing manufacturing process. The entire profile of the grid must be all steel or some other metal. Therefore, the excellent tensile and compression strengths of steel are only partially employed in the regions closest to the neutral axis. Attempts have been made to increase material efficiency by adding loops of steel in the bulb and to otherwise increase the amount of steel farthest from the neutral axis. All these efforts still employ steel in regions where the bending tensile or compression stresses approach zero psi.
Products based on composite technology have long been known in the art. More recently much attention has been given the use of fibers of a variety of sorts such as fiberglass, carbon, aramid, and boron in the reinforcement of polymers and polymer blends. The result has been a class of products that provide the highest strength to weight ratios. Pultrusion is a specific process developed to produce composite products using low viscosity polymers, usually thermosets, and continuous fiber strands. The fibers are immersed in a liquid polymer tank and then pulled through a die to generate a desired profile, hence, the name pul (PULl) trusion (exTRUSION). The resin is then cured. The result is a product with high strength in the machine direction and an overall high strength to weight ratio. Such technology has been used to produce suspension grid runners. These products have the additional advantage of being corrosion free when compared to those using steel. However, the cost premium is quite high reaching into that incurred when either aluminum or stainless steel is used to achieve corrosion free performance within the metal family of materials.